The commercial processing of photographic materials produces seasoned (used) solutions containing silver ions. Environmental regulations restrict the discharge of solutions containing silver to concentrations much less than the silver concentrations generally found in seasoned solutions. Thus the silver concentrations in seasoned solutions must be greatly reduced before discharge into the environment.
A much improved precipitation process for removal of silver from seasoned silver containing solutions is disclosed in U.S. Pat. No. 5,288,728. A trisodium salt of mercapto-s-triazine (TMT) is used to precipitate silver. It is believed that this salt is made according to method described in U.S. Pat. No. 5,075,444. The use of this salt in silver recovery provides an improvement over the prior art. Undesirable precipitates form in trisodium TMT solutions during storage. This requires filtration. This is a particular problem when making 15% trisodium TMT solutions from commercially available 55% trisodium TMT solids. Moreover, the commercially available material has an obnoxious sulfide odor.
No other alkali metal salts of TMT are available commercially. The method of U.S. Pat. No. 5,075,444 has not been used to make such other salts of TMT. It is believed that the method of this patent will only yield salts having an obnoxious sulfide odor.